Ring airfoil with parallel inner and outer surfaces

ABSTRACT

A ring airfoil with a voluminous leading edge region, an intermediate region, a trailing edge region including a flap. The ringed structural leading edge region combined with a rigid trailing edge region having intermediate discrete support portions extending therebetween provides sufficient rigidity to support the flap on the trailing edge region while using a membrane intermediate surface to form a portion of the intermediate region of the airfoil.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional ApplicationSer. No. 61/620,792, filed on Apr. 5, 2012 and U.S. ProvisionalApplication Ser. No. 61/763,805 filed on Feb. 12, 2013, respectively,the disclosures of which are incorporated herein by reference in theirentirety.

BACKGROUND

The present disclosure relates to the field of ring airfoils and moreparticularly to shrouded turbines comprising unique airfoilcharacteristics. More specifically, taught herein are embodimentsdirected to a modified ringed airfoil that provides a reduced crosssectional area for reduced side loads and reduced material use whilemaintaining performance. Airfoils with structural leading edges engagedwith substantially curved planar surfaces are common in the fields oflight aircraft and sailing vessels. Curved planar surfaces are definedas those that have an upper surface that is substantially parallel to alower surface. Such an airfoil has a reduced cross sectional area fromthat of an airfoil with continuous varying distance between the upperand lower surface. Utility scale wind turbines used for power generationhave one to five open blades comprising a rotor. Rotors transform windenergy into a rotational torque that drives at least one generator thatis rotationally coupled to the rotor either directly or through atransmission to convert mechanical energy to electrical energy.

A shrouded wind turbine has been described in U.S. patent applicationSer. No. 12/054,050, the disclosure of which is incorporated herein byreference in its entirety.

SUMMARY

The embodiments taught herein relate to a ringed airfoil with a crosssection that includes a leading edge portion with varying distancebetween the upper and lower surface, a symmetrical region havingsymmetry about the chord line through said symmetrical region wherein inone embodiment the upper surface is substantially parallel to a lowersurface, and a trailing edge region providing a flap on the trailingedge that is substantially perpendicular to the chord line of theairfoil. Providing a flap on the trailing edge of such an airfoilfurther reduces the cross sectional area of the airfoil compared toconvention air foils.

Lack of support structure(s) in an intermediate symmetrical region doesnot allow for a flap to function when configured perpendicular to thechord line of the resulting airfoil. Such a flap on the trailing edge ofa curved planar surface would flex until the flap failed to have anyeffect on the flow over the airfoil. In embodiments, taught herein, anorientation of the flap can be fixedly with respect to the chord line ofthe ring airfoil. For example, in one embodiment, the ring airfoil caninclude a rigid trailing edge that provides sufficient structure for aflap that is disposed substantially perpendicular to the chord of theairfoil.

In one embodiment, an aerodynamically contoured ring airfoil isdisclosed. A body extends circumferentially about a center axis havingan aerodynamic structure formed by an outer surface and an innersurface. The outer and inner surfaces extend axially with respect to thecenter axis along a camber line. The body includes a leading edgeregion, a trailing edge region, and an intermediate region extendingbetween the leading edge region and the trailing edge region. Theleading edge region having a non-uniform cross-sectional thicknessextending along the camber line defined by the outer surface and theinner surface of the body. The trailing edge region includes a flapextending therefrom and orientated at an angle with respect to a chordline of the body to allow a fluid flow flowing along the inner surfaceto remain attached to the inner surface.

In one example, embodiment, an energy extracting shrouded fluid turbineis disclosed that includes an energy extracting assembly and an airfoil.The energy extracting assembly includes a rotor disposed radially abouta center axis. The airfoil has a body extending circumferentially aboutthe center axis. The body has an aerodynamic structure formed by anouter surface and an inner surface. The outer and inner surfaces extendaxially with respect to the center axis along a camber line. The bodyincludes a leading edge region a trailing edge region, and anintermediate region that extends between the leading edge region and thetrailing edge region. The leading edge region has a non-uniformcross-sectional thickness extending along the camber line defined by theouter surface and the inner surface of the body. The trailing edgeregion includes a flap extending therefrom and orientated at an anglewith respect to a chord line of the body to allow a fluid flow flowingalong the inner surface to remain attached to the inner surface.

In some embodiments, the flap extends from the trailing edge regionperpendicularly to the chord line, has a length of about one-tenth toabout one-third a length of the chord line, and/or includes at least oneperforation to permit fluid flow through the flap.

In some embodiments, the flap extends from a trailing edge of theairfoil.

In some embodiments, the flap extends between a first ring structure anda second ring structure, the first and second ring structures providinga hoop strength to the flap.

In some embodiments, the first ring structure provides a hoop strengthto the trailing edge region of the body.

In some embodiments, the intermediate region includes at least oneintermediate support portion extending between the leading edge regionand the trailing edge region. In some embodiments, the intermediatesupport portion is composed of a rigid material and/or has a uniformcross-sectional thickness extending along the mean camber line definedby the outer surface and the inner surface of the body.

In some embodiments, the intermediate region includes at least oneintermediate membrane portion extending between the leading edge regionand the trailing edge region. In some embodiments, the intermediatemembrane portion has a uniform cross-sectional thickness extending alongthe mean camber line defined by the outer surface and the inner surfaceof the body and/or is composed of a non-rigid material.

In some embodiments, the intermediate support portions providestructural support to the intermediate membrane portion.

Any combination or permutation of embodiments is envisioned. Otherobjects and features will become apparent from the following detaileddescription considered in conjunction with the accompanying drawings. Itis to be understood, however, that the drawings are designed as anillustration only and not as a definition of the limits of the presentdisclosure.

BRIEF DESCRIPTION

The present disclosure relates to a ringed airfoil having a uniqueairfoil cross sectional shape with rigid portions at the leading andtrailing edges, providing hoop strength that supports a membraneintermediate portion and allows for a trailing edge flap. In exampleembodiments, a combination rigid structural portions and non-rigidmembrane portions can be used to form an example ring airfoil thatprovides for controlling a boundary layer at the trailing edge of theairfoil and provides for increased suction through the center of thering airfoil compared to conventional ring airfoils. Such an airfoilprovides a means of utilizing lightweight materials while generatingaerodynamic circulation resulting in a pressure differential on theinside of the ring airfoil as compared to the exterior of the airfoil.

In one embodiment, the ring airfoil surrounds a rotor and electricalgeneration equipment of a shrouded fluid turbine. The fluid turbine mayhave a single shroud, or may include multiple shrouds. The shrouds arecomprised of generally ring airfoils that may include a turbine shroudand an ejector shroud.

In one embodiment, the turbine shroud houses a rotor and includes mixingelements at the trailing edge of the ring airfoil that are in fluidcommunication with an ejector shroud fluid stream providing amixer-ejector pump. The shroud(s) generate aerodynamic circulationresulting in suction on the inside of the turbine shroud and are part ofa tightly coupled system that, combined with the mixer-ejector pump,allow the acceleration of more air through the turbine rotor than thatof un-shrouded designs, thus increasing the amount of power that may beextracted by the rotor.

In the field of fluid dynamics, the term “stall” refers to the conditionin which fluid flow separation occurs. In other words, the fluid flowingclosely around the airfoil starts to detach from the surface and becometurbulent. The embodiments taught herein are described be described inview of a mixer only embodiment and a mixer-ejector turbine embodiment.One skilled in the art will recognize that the example embodiments ofthe present disclosure may be readily applied to any ringed airfoilincluding any number of ducted or shrouded fluid turbine applications.The recitation of a mixer only embodiment and a mixer-ejector turbineembodiment is therefore not intended to be limiting in scope as issolely for convenience in illustrating an example embodiment of thepresent disclosure. Separation of airflow from the aerodynamic surfacesthrough a mixer turbine and/or Mixer-Ejector Turbine (MET) can besubstantially prevented to advantageously maintain an efficiency of theturbine and to advantageously mitigate diffuser stall.

The Kutta-Joukowski theorem describes the circulation around any closedsurface. It is this circulation that causes lift and increases the airflow through the shrouded turbine. The theorem determines the liftgenerated by one unit of span in a closed body and states that when thecirculation Γ_(∞) is known, the lift L per unit span (or L′) of acylinder can be calculated using the following equation:

L′=ρ _(∞) V _(∞)Γ_(∞)  Equation 1

where ρ_(∞) and V_(∞) are the fluid density and the fluid velocity farupstream of the cylinder, respectively. The circulation Γ_(∞) is definedas a line integral in the following equation:

$\begin{matrix}{\Gamma_{\infty} = {\oint_{C_{\infty}}{V\; \cos \; \theta \; {s}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Improved circulation through the use of an aerodynamic modified region(AMR) on the trailing edge of the mixer and/or ejector shroud airfoilprovides for increased performance of the shrouded turbine. The Kuttacondition (as a function of the Kutta-Joukowski theorem) controlscirculation generated by the airfoil and generally prevents flowseparation from the aerodynamic surfaces until the flow reaches thetrailing edge.

Fluid moves through or across an airfoil shape and produces anaerodynamic force. The component of the aerodynamic force that isperpendicular to the direction of fluid flow is called lift and thecomponent parallel to the direction of fluid flow is called drag.Additionally, an airfoil has a suction surface and a pressure surfacethrough which lift forces are generated. The airfoil suction side isdefined by the airfoil surface turning away from the oncoming flow.Usually the top (or outer) and bottom (or inner) airfoil surface arejoined by a curved leading edge and a sharp trailing edge. The camberline of the airfoil dissects this trailing edge at one end and extendsto the apex, or most upwind point, of the leading edge. Aerodynamiccirculation is a result of flow turning and is usually limited by flowseparation on the airfoil suction side.

An example embodiment of the present disclosure provides for obtainingincreased airfoil circulation, or effective flow turning, as compared toconventional airfoil structures by modifying the airflow across thepressure side of the airfoil aerodynamic surfaces, especially proximateto the trailing edge. In example embodiments of the present disclosure,an increase in circulation can be accomplished by increasing surfaceturning on the pressure side of the airfoil. Increasing the turning onthe pressure side is possible because the surface is turning into theflow direction and the flow is less apt to separate from the surface onthe pressure side. In one embodiment, increasing the flow turning can beachieved using a trailing edge flap on the top (or outer) surface of theairfoil (i.e., the pressure side).

In example embodiments, the flap can be a flat plate or other protrusionfrom the trailing edge. In some embodiments, a length of the trailingedge flap can be on the order of 1-30% of a length of the airfoil chordextending between the leading edge and the trailing edge of the airfoil.The trailing edge flap can be oriented perpendicular to the chord lineand disposed on the airfoil pressure side at or proximate to thetrailing edge. In some embodiments the trailing edge flap is perforated.The perforations can allow the flap to provide an effective height tocause increased circulation while also providing reduced drag.

The use of a flap effectively changes the flow-field in the region ofthe trailing edge of the ring airfoil by introducing contra-rotatingvortices aft of the flap, which alters the Kutta condition andcirculation in the region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front, perspective view of an example ring airfoil of thepresent disclosure.

FIG. 2 is a side, cross sectional view of the example airfoil of FIG. 1.

FIG. 3 is a side, cross sectional view of the example airfoil of FIG. 1.

FIG. 4 is a side, detail, cross sectional view of the example airfoil ofthe embodiment of FIG. 1.

FIG. 5 is a side, cross sectional view of the example airfoil of theembodiment of FIG. 1 with flow lines.

FIG. 6 is a front, perspective view of another example ring airfoil ofthe present disclosure.

FIG. 7 is a side, cross sectional view of the example airfoil of FIG. 6.

FIG. 8 is a front, right, perspective view of an example shroudedturbine for which the turbine shroud corresponds to the example airfoilof FIG. 1.

FIG. 9 is a front, right, perspective view of an example shroudedturbine for which the turbine shroud corresponds to the example airfoilof FIG. 6.

FIG. 10 is a front, right, perspective view of an example mixer-ejectorturbine incorporating the example airfoils of FIGS. 1 and 6.

FIG. 11 is a rear, right, perspective view of an example mixer-ejectorturbine of FIG. 10.

FIG. 12 is a side, perspective, detail cross section of an examplemixer-ejector turbine of FIG. 10 and FIG. 11, cut through the outwardturning mixer airfoil section.

FIG. 13 is a side, perspective, detail cross section of themixer-ejector turbine of FIG. 10 and FIG. 11, cut through the inwardturning mixer airfoil section.

FIG. 14 is a detailed view of the flaps disposed on a trailing edgeregions of the example mixer ejector turbine of FIG. 10 and FIG. 11.

FIG. 15 is a front, right, perspective view of another examplemixer-ejector turbine for which the turbine shroud and the ejectorshroud have a faceted configuration.

FIG. 16 is a side, perspective, detail cross section of an examplemixer-ejector turbine of FIG. 15, cut through the outward turning mixerairfoil section.

FIG. 17 is a front, right, perspective view of another example shroudedturbine for which the turbine shroud has a faceted configuration.

DETAILED DESCRIPTION

A more complete understanding of the components, processes, andapparatuses disclosed herein can be obtained by reference to theaccompanying figures. These figures are intended to demonstrate thepresent disclosure and are not intended to show relative sizes anddimensions or to limit the scope of the example embodiments.

Although specific terms are used in the following description, theseterms are intended to refer only to particular structures in thedrawings and are not intended to limit the scope of the presentdisclosure. It is to be understood that like numeric designations referto components of like function.

The term “about” when used with a quantity includes the stated value andalso has the meaning dictated by the context. For example, it includesat least the degree of error associated with the measurement of theparticular quantity. When used in the context of a range, the term“about” should also be considered as disclosing the range defined by theabsolute values of the two endpoints. For example, the range “from about2 to about 4” also discloses the range “from 2 to 4.”

A shrouded turbine can include a turbine shroud with or without mixinglobes on a trailing end of the turbine shroud. As set forth previously,a shrouded turbine that includes a mixer shroud is one suitable exampleof a ringed airfoil in which the example embodiments of the presentdisclosure may be utilized. The turbine shroud includes a camberedshroud, wherein the shroud is a substantially ringed airfoil. Theturbine shroud contains a rotor, which extracts power from a primaryfluid stream. The turbine shroud provides for increased flow through therotor allowing increased energy extraction due to higher flow ratescompared to shroudless fluid turbines.

A Mixer-Ejector Turbine (MET) can provide an improved means ofgenerating power from fluid currents using a mixer/ejector pump. As setforth previously, a MET is one suitable example of a ringed airfoil inwhich the example embodiments of the present disclosure may be utilized.The Mixer-Ejector Turbine includes tandem cambered shrouds, wherein eachshroud is a substantially ringed airfoil, and a mixer/ejector pump. Theprimary shroud contains a rotor, which extracts power from a primaryfluid stream. The tandem cambered shrouds and ejector provide forincreased flow through the rotor allowing increased energy extractiondue to higher flow rates compared to shroudless fluid turbines. Themixer/ejector pump transfers energy from the bypass flow to the rotorwake flow allowing higher energy per unit mass flow rate through therotor. These two effects enhance the overall power production of theturbine system.

The term “rotor” is used herein to refer to any assembly in which one ormore blades are attached to a shaft and able to rotate, allowing for theextraction of power or energy from wind rotating the blades. Examplerotors include a propeller-like rotor or a rotor/stator assembly. Anytype of rotor may be enclosed within the turbine shroud in the fluidturbine of the present disclosure.

The leading edge of a shroud may be considered the front of an airfoil,and the trailing edge of an airfoil may be considered the rear of theairfoil. A first component of the airfoil located closer to the front ofthe airfoil may be considered “upstream” of a second component locatedcloser to the rear of the airfoil (i.e. the second component is“downstream” of the first component). Furthermore, the term “innersurface” is used herein to define a surface of ring airfoil that isinwardly facing towards a center axis of the airfoil. The term “outersurface” is used herein to define a surface that is outwardly facingaway from the center axis of the airfoil such that the inner surface iscloser to the center axis than the outer surface. Likewise, the term“suction side” or “low pressure side” of the ring airfoil is used hereinto refer to the interior of the airfoil (i.e. radially inward of theinner surface) and the term “pressure side” of the airfoil is usedherein to refer to exterior of the airfoil (i.e. radially outward fromthe outer surface).

The term “hoop strength” is used herein to refer to an ability of astructure to resist radially deformational forces about a circumferenceof a generally cylindrical or ring shaped structure and providedimensional stability. For example, example embodiments of an airfoildescribed herein can include a rigid trailing edge region having a hoopstrength to resist deformational forces of a fluid flow.

In one embodiment, the present disclosure relates to a ring airfoil thatincludes a generally rigid structural leading edge region, anintermediate region formed of structurally rigid and non-rigid portions,and a generally rigid structural trailing edge region. The ring airfoilfurther comprises a flap on the trailing edge portion that issubstantially perpendicular to the chord of the airfoil. An orientationof the flap with respect to the chord line can be fixed. In oneembodiment, an exemplary embodiment of the ring airfoil can beimplemented as a turbine shroud or a turbine mixer shroud that includesinward and outward turning segments that surround a rotor and/or anexample embodiment of the ring airfoil can be implemented as an ejectorshroud that generally surrounds an exit of a turbine shroud or a turbinemixer shroud.

FIG. 1 is a front perspective view of an example ring airfoil 100. Theairfoil 100 can have a body 102 extending circumferential about a centeraxis 105. The body 102 includes a leading edge region 112, anintermediate region 115 having one or more intermediate membraneportions 138 and one or more intermediate support portions 139, and atrailing edge region 116 having a flap 136. The leading edge region 112can include a leading edge 162 of the airfoil 100 and the trailing edgeregion 116 can include a trailing edge 166 of the airfoil 100. The oneor more intermediate portions 138 and 139 of the intermediate region 115can extend between the leading edge region 112 and the trailing edgeregion 116 to mechanically couple the leading edge region 112 to thetrailing edge portion 116. The one or more intermediate membraneportions 138 can be formed of one or more semi-rigid and/or non-rigidmaterials, e.g., as discussed herein, and the one or more intermediatesupport portions 139 can be formed of one or more a semi-rigid and/orrigid materials, e.g., as discussed herein. In an example embodiment,the ringed structurally rigid leading edge region combined with therigid trailing edge region and intermediate discrete support portionsprovide sufficient rigidity to support the flap 136 on the trailing edgeregion 116 in a fixed relationship to a chord line and cambered linewhile implementing the intermediate membrane portion(s) to form surfacesof the intermediate region 115 of the airfoil 100. Thus, the structureof the airfoil 100 facilitates a fixed angular relationship between theflap 136 and the chord line 140 as well as between the flap 136 and themean cambered line 170. Example embodiments of the airfoil 100 includinga flap as described herein (e.g., flaps 136 and 236) can result in aringed airfoil that exhibits similar performance characteristics as aconventional airfoils that have a greater chord length and no flap.

In an example embodiment, the one or more intermediate support portions139 can provide structural support to the body 102 between the leadingedge portion 112 and the trailing edge portion 116. The intermediatesupport portions 139 can be spaced apart from each other and can bedistributed discretely and circumferentially about the center axis 105.The intermediate support portions 139 can be dimensioned and/orconfigured to specify a spatial relationship between the leading edgeportion 112 and the trailing edge portion 116 and/or a shape of the oneor more intermediate membrane portions 138. As one example, in oneembodiment, the one or more intermediate support portions 139 can set adistance between the leading edge and the trailing edge of the airfoil100, which corresponds to a chord line of the airfoil 100. As anotherexample, in one embodiment, the intermediate support portions 139 can becontoured to taper away from the center axis 105 towards the trailingedge region 116 such that a diameter of the trailing edge portion islarger than a diameter of the leading edge portion 112. In someembodiments, the one or more intermediate membrane portions 138 cangenerally conform to the contours of the intermediate support portions139. In some embodiments, the one or more intermediate portions 138 canbe contoured independently of the one or more intermediate supportportions.

In some embodiments, the leading edge region 112, the trailing edgeregion 116, and the one or more intermediate support portions 139 can beintegrally formed as a single integral unit, and the one or moreintermediate membrane portions 138 can be separately attached to formthe body 102. In some embodiments, the leading edge region 112, thetrailing edge region 116, the one or more intermediate portions 138, andthe one or more intermediate support portions 139 can be separatecomponents that are mechanically coupled together to form the body 102.

Some examples of plastic materials that can be used to form the leadingedge region 112, the trailing edge region 116, and/or the one or moreintermediate support portions 139 of the airfoil 100, or portionsthereof, can include, but are not limited to polymers, such as apolyolefin or a polyamide, carbon composites, and/or metals. Someexamples of polyolefins include polypropylene and polyethylene, such ashigh density polyethylene (HDPE) and low density polyethylene (LDPE).Some examples of polyamides include nylons. In some embodiments,polyvinyl chloride and plastisols can be used to form the leading edgeregion 112 and trailing edge region 116.

Some examples of materials that can be used to form the intermediatemembrane portions 138 can include, but are not limited to fabrics,polymeric films, thin metal sheets, thin composites, marine shrink wrap,and the like. For embodiments in which fabric used, the fabric can beimpregnated with a polymer resin (such as polyvinyl chloride) or apolymer film (such as modified polytetrafluoroethylene). Some examplesof polymeric films include, but are not limited to polyvinyl chloride(PVC), polyurethane, polyfluoropolymers, multi-layer films of similarcomposition, and the like. Polyurethane films can be durable and canhave good weatherability. Aliphatic versions of polyurethane films canbe generally resistant to ultraviolet radiation. Some examples ofpolyfluoropolymers include polyvinyldidene fluoride (PVDF) and polyvinylfluoride (PVF). Commercial versions are available under the trade namesKYNAR® and TEDLAR®. Polyfluoropolymers generally have very low surfaceenergy, which allow their surface to remain somewhat free of dirt anddebris, and can shed ice more readily as compared to materials having ahigher surface energy.

In example embodiments, the material or materials used to form theairfoil 100 and/or portions thereof can be reinforced with a reinforcingmaterial, such as, for example, highly crystalline polyethylene fibers,paramid fibers, and polyaramides.

The leading edge region 112, the trailing edge region 116, the one ormore intermediate support portions 138, and/or the one or moreintermediate membrane portions 139 can be formed of multiple layers ofmaterial, for example, comprising two, three, or more layers.Multi-layer constructions may add strength, water resistance,ultraviolet (UV) stability, and other functionality.

In some embodiments, the leading edge region 112 of the airfoil can be asandwich composite material, such as an epoxy-impregnated e-glass matte,and the space inside the sandwich composite can be filled with foam.This configuration provides for high beam stiffness construction withoverall low density.

FIG. 2 is a cross sectional view of an example embodiment of a ringairfoil of the present disclosure along the line 2-2 of FIG. 1 depictingone of the intermediate membrane portions 138 of the airfoil 100. Theleading edge region 112 can extend from the leading edge 162 to theintermediate region 115. The leading edge region 112 can have avolumetric form with varying thickness T_(L) between the inner surface132 (i.e. suction side surface 132) and the outer surface 134 (i.e.pressure side surface 134), thus creating a volume of varying thicknessT_(L). The leading edge 162 of the airfoil 100 can be generally rounded,bull-nosed, or otherwise shaped to form an aerodynamic surface fordividing a fluid into at least two flows or streams (e.g., a suctionside along the inner surface 132 and a pressure side along the outersurface 134. The cross-sectional shape of the leading edge region 112can taper away from the leading edge 162 increasing in cross-sectionalthickness T_(L) and then can taper towards a center or mean camber line170 decreasing in cross-sectional thickness T_(L) to a joint 131 betweenthe intermediate membrane portion 138 along the mean camber line 170such that the cross-sectional thickness T_(L) of the leading edge region112 generally varies from the leading edge 162 to joint 131 mechanicallycoupling the leading edge region 112 to the intermediate membraneportions 138. The center or mean camber line 170 is generally positionedmidway between outer and inner surfaces 132 and 134 of the airfoil 100,respectively, along the longitudinal extent of the airfoil 100.

As depicted in FIG. 2, a chord 140 defines a length of the airfoil 100between the leading edge 162 and the trailing edge 166 of the airfoil100, which can be determined based on the mean camber line 170. Across-sectional thickness of the airfoil 100 can correspond to adistance from the outer surface 134 to the inner surface 132 of theairfoil 100, measured perpendicular to the mean camber line 170, and canvary with distance along the mean camber line 170 such that thecross-sectional thickness of the airfoil 100 varies over a length of theairfoil 100 from the leading edge 162 to the trailing edge 166. Aninterior area (or volume) 113 formed by the surfaces 132, 134 in theleading edge region 112 can be hollow, or can be filled with supportmembers for providing structural rigidity and shape. In accordance withone embodiment, a foam material 172 may be utilized in providing bothshape and structural rigidity to the assembly.

In some embodiments, the one or more intermediate membrane portions 138of the intermediate region 115 can extend linearly from the leading edgeregion 112 to the trailing edge region 116. In some embodiments, theintermediate membrane portions 138 can have a curvature between theleading edge region 112 and the trailing edge region 116. Theintermediate membrane portions 138 can have a substantially uniform andconstant cross-sectional thickness T_(IM) along its length. In theexample embodiment, the surfaces 132, 134 can be positioned adjacent toeach other and can be in contact to form the intermediate membraneportions 138 such that the cross-sectional thickness T_(IM) of theintermediate membrane portions 138 can be approximately equal thethickness of the material or materials between the surfaces 132, 134. Insome embodiments, the intermediate membrane portions 138 can be formedof a sheet of material with a thickness such that no space or voidexists in the intermediate membrane portions 138. For example, theintermediate membrane portions 138 can be a curved planar form withrelatively constant thickness.

In one example embodiment, the intermediate membrane portions 138 can betacked, adhered, friction fit, or otherwise attached or fixed to theleading edge region 112 to secure the intermediate membrane portions 138to the leading edge region 112. In one example embodiment, the joint 131between the leading edge region 112 and the intermediate membraneportions 138 can be formed by a groove or channel 117 configured toreceive and hold an upstream end 143 of the intermediate membraneportions 138. For example, the upstream end 143 can have a circularcross section corresponding to a circular cross section of the channel117 such that the upstream end 143 of the intermediate membrane region138 can slide into, engage, and be retained by the channel 117 of theleading edge region 112.

In example embodiments, the trailing edge region 116 can be formed as aringed structure extending circumferentially about the center axis 105and the trailing edge 116 can have a diameter or width that is greaterthan a diameter or width of the leading edge 162. An end of the trailingedge region 116 opposite of the trailing edge 166 can include a recessedportion, such as a notch or channel 182 configured to receive andmechanically couple to the intermediate membrane portions 138. In anexample embodiment, the trailing edge region can provide rigidity to thetrailing edge 166 of the airfoil 100 such that the trailing edge 166.

The trailing edge region 116 can include the flap 136 extendingtherefrom. In one example embodiment, the flap 136 can extend radiallyoutward from or proximate to the trailing edge 166. The flap 136 canhave a length L that extends at an angle 0 with respect to the chordline 140. In an example embodiment, the angle 0 between the chord line140 and the flap 136 can be fixed. The length L of the flap 136 can beabout ten to about thirty percent less than a length of the chord line140. In an example embodiment, the length L of the flap 136 can extendperpendicularly to the chord line 140 and can be implemented to turn theairflow along the outer surface 134. In example embodiments, the flap136 can include perforations 184 to allow some air to flow through theflap 136 to reduce the force exerted on the flap by the airflow. Inexemplary embodiments, the flap 136 can be formed of the same or asimilar material as the intermediate membrane portions 138.

FIG. 3 is a cross sectional view of the airfoil of FIG. 1 along the line3-3 of FIG. 1 depicting one of the intermediate support portions 139 ofthe intermediate region 115, which can be disposed between and betweenthe leading edge region 112 and the trailing edge region 116. In oneexample embodiment, as depicted in FIG. 3, the intermediate supportportions 139 can be integrally formed with the leading edge region 112such that the intermediate support portions 139 forms a unitarystructure with the leading edge region 112 and the intermediate supportportions 139 can be mechanically coupled to the trailing edge region116. In another example embodiment, the intermediate support portions139 can be mechanically coupled to the leading edge region 112 and/orthe trailing edge region 116. In yet another example embodiment, theintermediate support portions 139 can be integrally formed with theleading edge region 112 and/or the trailing edge region 116.

The intermediate support portions 139 can provide structural support forthe air foil 100 to define a distance between the leading edge region112 and the trailing edge region 116 and/or can provide a supportstructure for the intermediate membrane portions 139, e.g., to define acontour of the intermediate membrane portions 138. The intermediaterigid portions 139 can be elongate members have a generally rod-like orbar-like configuration. The intermediate support portions 139 can beconfigured to engage the channel 182 formed in the trailing edge region116 to mechanically couple the intermediate support portions 139 to thetrailing edge region 116. In some embodiments the intermediate supportportions can be integrally formed with the leading edge region 112and/or the trailing edge region 116.

In some embodiments, the intermediate support portions 139 can extendlinearly from the leading edge region 112 to the trailing edge region116. In some embodiments, the intermediate support portions 139 can havea curvature between the leading edge region 112 and the trailing edgeregion 116. The intermediate support portions 139 can have asubstantially uniform and constant cross-sectional thickness T_(IS)along the length. In the example embodiment, the surfaces 132, 134 ofthe intermediate support portions 139 can be positioned adjacent to eachother and can be in contact to form the intermediate support portions139 such that the cross-sectional thickness T_(IS) of the intermediatesupport portions 139 can be approximately equal the thickness of thematerial or materials between the surfaces 132, 134. In someembodiments, the intermediate support portions 139 can be formed of asheet of material with a thickness such that no space or void exists inthe intermediate support portions 139. For example, the intermediatesupport portions 139 can be a curved planar form with relativelyconstant thickness.

In one embodiment, the intermediate membrane portions 138 can encompassor encircle the intermediate support portions 139. In some embodiments,the intermediate membrane portions 138 can be tacked, adhered, frictionfit, or otherwise attached or fixed to the intermediate support portions139 to secure the intermediate membrane portions 138 to the intermediatesupport portions 139. For example, in one embodiment, a polyethyleneshrink wrap can be used as the intermediate membrane portion(s) 138, andthe polyethylene shrink wrap can encircle the intermediate supportportions 139 and heat can be applied to the polyethylene shrink wrap toshrink the polyethylene shrink wrap onto the intermediate supportportions 139 forming a tight friction fit. In some embodiments, theintermediate membrane portions 138 can each extend between a pair ofintermediate support portions 139 from the leading edge region 112 tothe trailing edge region 116.

Referring to FIG. 4, an orthographic detail section view of trailingedge region 116 of the airfoil 100 of FIG. 2 is depicted. The exampleembodiment includes the flap 136 on the trailing edge 116. The flap 136is generally perpendicular, or in other words, is at the angle θ betweenapproximately 85° and 120° relative to the chord line 140 of the airfoilcross section. In some embodiments the trailing edge region 116 caninclude a rigid member 148 that engages the membrane intermediateportion 138 (e.g., via channel 182). The rigid member 148 is engagedwith a ring 146 that is in turn engaged with a flap 136. The ring 146provides hoop strength to the rigid member 148. The flap 136 contains atleast one ring 144 that provides hoop strength to the outer edge of theflap 136. As discussed above, rigid structural support members in theform of the intermediate support portions 139 are spaced radially aboutthe ringed airfoil proximal to intermediate membrane portions 138 (FIGS.1 and 3). The intermediate support portions 139 provide structure tosupport the location and configuration of the trailing edge 116. Thestructural support provided by the intermediate support portions 139maintains the angle θ of the flap 136 with respect to the chord 140 andprovides a structure to support the membrane intermediate portions 138.

Referring to FIG. 5, an orthographic cross section of a ring airfoil ofan example embodiment 100 is depicted. The direction and path of fluidflow around the airfoil 100, from the leading edge 112 to the trailingedge 116 is represented by arrow 152 on the suction side 132 (i.e. theinner surface 132), and arrow 154 on the pressure side 134 (i.e. theouter surface).

Referring again to FIG. 5, the flap 136 causes an area of stagnation 141in the flow on the pressure side of the airfoil 134. The addition of theflap 136 on or proximate to the trailing edge 166 of the airfoil 100also generates vortices 118 downwind of the trailing edge 116 of theairfoil 100. The addition of the flap 136 causes the air stream 154 onthe pressure side 134 of the airfoil 100 to be pushed upward thusallowing the fluid stream 152 on the suction side 132 of the airfoil 100to stay attached to the surface and generate improved circulation of thefluid streams.

FIG. 6 depicts a perspective view of another example airfoil 200. A body202 of the airfoil 200 can include a leading edge region 212, anintermediate region 215, and a trailing edge region 216. The airfoil 200can include mixing elements 226, 228 that may be formed by theintermediate region 215 and the trailing edge region 216. As depicted,the mixing lobes may include low energy mixing lobes 228 that extendinward toward the central axis 205, and high energy mixing lobes 226that extend outward away from the central axis 105. In other words, thetrailing edge 124 of the turbine shroud 104 is shaped to form twodifferent sets of mixing lobes. The mixing lobes 126, 128 can form ageneral circular crenellated or circumferential undulating in-and-outshape about the center axis 205.

The trailing edge region 216 of the airfoil 200 can be formed of a rigidmaterial and can have a general circular crenellated or circumferentialundulating in-and-out shape about the center axis 205, which can importthe structural configuration of the mixing lobes 126, 128 tointermediate membrane portions 238 of the intermediate region 215. Thetrailing edge region can include one or more flaps 236. In an exampleembodiment, as depicted in FIG. 6, each low energy mixing lobe 228 caninclude one of the flaps 236 and high energy mixing lobes 226 can bedevoid of the flap 236. In another example embodiment, the high energyand low energy mixing lobes 226, 228 can include a flap 236. In yetanother example embodiment, the flap 236 can extend continuously alongthe trailing edge region 216 to form a single flap continuously disposedabout the center axis 205. In an example embodiment, the ringedstructural leading edge region 212 combined with the rigid trailing edgeregion 216 and intermediate discrete support portions of theintermediate region 215 provide sufficient rigidity to support the flap136 on the trailing edge region 116 in a fixed relationship to the chordline while implementing the intermediate membrane portion(s) as to formthe surfaces of the intermediate region of the airfoil. Thus, thestructure of the airfoil 100 facilitates provide a fixed angularrelationship between the flap 136 and the chord line 140 as well asbetween the flap 136 and the mean cambered line 170. Example embodimentsof the airfoil 200 including the flap 236 can result in a ringed airfoilthat exhibits similar performance characteristics as a conventionalairfoils that have a greater chord length and no flap.

In an example embodiment, the one or more intermediate support portions239 can provide structural support to the body 202 between the leadingedge portion 212 and the trailing edge portion 216. The intermediatesupport portions 239 can be spaced apart from each other and can bedistributed discretely and circumferentially about the center axis 205.The intermediate support portions 239 can be dimensioned and/orconfigured to specify a spatial relationship between the leading edgeportion 212 and the trailing edge portion 216. As one example, in oneembodiment, the one or more intermediate support portions 239 can set adistance between the leading edge and the trailing edge of the airfoil200, which corresponds to a chord line of the airfoil 200.

FIG. 7 is a cross sectional view of the airfoil 200 of FIG. 6 along theline 7-7. As depicted in FIG. 7, the cross section of the airfoil 200generally corresponds to the cross-section of the airfoil 100 in thatthat the leading edge region includes a varying volume and theintermediate membrane portion(s) 238 includes a generally uniformvolume. The leading edge 262 of the airfoil 100 can be generallyrounded, bull-nosed, or otherwise shaped to form an aerodynamic surfacefor dividing a fluid into at least two flows or streams (e.g., a suctionside along the inner surface 232 and a pressure side along the outersurface 234. The cross-sectional shape of the leading edge region 212can taper away from the leading edge 262 increasing in cross-sectionalthickness and then can taper towards a center or mean camber line 270decreasing in cross-sectional thickness to the intermediate region alongthe mean camber line 270. The center or mean camber line 270 isgenerally positioned midway between outer and inner surfaces 232 and 234of the airfoil 200, respectively, along the longitudinal extent of theairfoil 200.

As depicted in FIG. 7, a chord 240 defines a length of the airfoil 200between the leading edge 262 and the trailing edge 266 of the airfoil200, which can be determined based on the mean camber line 270. Theintermediate membrane portion 238 can have a substantially uniform andconstant cross-sectional thickness along its length. In the exampleembodiment, the surfaces 232, 234 can be positioned adjacent to eachother and can be in contact to form the intermediate membrane portion238.

Similar to the intermediate region 115 of the example airfoil 100described herein, the intermediate region 215 can include intermediatemembrane portions 238 and intermediate support portions 239. Theintermediate membrane portions 238 can be formed of semi-rigid and/ornon-rigid materials and the intermediate support portions 239 can beformed of semi-rigid and/or rigid materials. The intermediate region 215provides the transitional area between the inward turning mixingelements 226 and the outward turning mixing elements 228. The rigidtrailing edge region 216 provides the structure to support the membranesurfaces that make up the mixing elements 226 and 228. In exampleembodiments, the trailing edge region 216 can be formed as a rigidstructure extending about the center axis 205 in the circumferentialundulating manner. In an example embodiment, the trailing edge region216 can provide rigidity to the trailing edge 266 of the airfoil 200such that the trailing edge 266.

The trailing edge region 216 can include the flap 236 extendingtherefrom. In one example embodiment, the flap 236 can extend radiallyoutward from or proximate to the trailing edge 266. The flap 236 canhave a length L that extends at an angle θ′ with respect to the chordline 240. In an example embodiment, the angle θ′ between the chord line140 and the flap 236 can be fixed and/or the length L of the flap 236can be about ten to about thirty percent less than a length of the chordline 240. In an example embodiment, the length L of the flap 236 canextend perpendicularly to the chord line 240 and can be implemented toturn the airflow along the outer surface 234. In the present exampleembodiment, the flap 236 is engaged with the trailing edge 266 of theoutward turning mixing elements 228. The trailing edge 266 is comprisedof similar components as depicted and described in FIGS. 3-4. In exampleembodiments, the flap 236 can include perforations 284 to allow some airto flow through the flap 236 to reduce the force exerted on the flap 236by the airflow. The flap 236 is dimensioned and configured to allow afluid flow flowing along the inner surface to remain attached to theinner surface.

FIG. 8 depicts a front perspective view of an example shrouded fluidturbine 300 in the form of a wind turbine having a support structure302, an energy extracting assembly 345 and a turbine shroud formed bythe example airfoil 100 having the leading edge region 112, theintermediate region 115, and the trailing edge region 116. The energyextracting assembly 345 can include a nacelle body 350 and a rotor 340.The rotor 340 is engaged with the nacelle body 350 at the proximal endof the rotor blades. The airfoil 100 can encircle the rotor 340. In oneexample, embodiment the leading edge 166 of the airfoil 100 can bepositioned up stream of the rotor 340 and/or the trailing edge 166 ofthe airfoil 100 can be positioned downstream of the rotor 340. Theleading edge 162 can form an inlet of the shrouded fluid turbine 300 andthe trailing edge 166 can form the exhaust of the shrouded fluid turbine300. The flap 136 can allow a fluid flow (e.g., airflow) flowing alongthe inner surface of the air foil to remain attached to the innersurface. In an example embodiment, the airfoil 100 can be positionedrelative to the nacelle body 350 and rotor 340 using elongate supportstructures 307 such that the nacelle body 350, the rotor 340, and theairfoil 100 are position coaxially with respect to each other about thecenter axis 105.

FIG. 9 depicts a front perspective view of an example shrouded fluidturbine 400 in the form of a wind turbine having the support structure302, the energy extracting assembly 345, and a turbine mixer shroudformed by the example airfoil 200 having the leading edge region 212,the intermediate region 215, and the trailing edge region 216. Theairfoil 200 can encircle the rotor 340. In one example, embodiment theleading edge 266 of the airfoil 200 can be positioned up stream of therotor 340 and/or the trailing edge 266 of the airfoil 200 can bepositioned downstream of the rotor 340. The leading edge 262 can form aninlet of the shrouded fluid turbine 400 and the trailing edge 266 canform the exhaust of the shrouded fluid turbine 400. As described above,the trailing edge 266 includes inward turning mixing elements 226 andoutward turning mixing elements 228. The inward turning mixing elements226 curve inward toward the central axis 205 and the outward turningmixing elements 228 curve outward from the central axis 205. The flap236 can allow a fluid flow (e.g., airflow) flowing along the innersurface of the air foil to remain attached to the inner surface. In anexample embodiment, the airfoil 200 can be positioned relative to thenacelle body 350 and rotor 340 using elongate support structures 307such that the nacelle body 350, the rotor 340, and the airfoil 200 areposition coaxially with respect to each other about the center axis 205.

FIG. 10 is a front, perspective view of an example embodiment of ashrouded fluid turbine 500 incorporating example embodiments of the ringairfoils 100 and 200 of the present disclosure. FIG. 11 is a rear,perspective view of the shrouded fluid turbine of FIG. 10. FIG. 12 is aside perspective, detail, section view of the shrouded fluid turbine 500of FIGS. 10 and 11 cut through the outward turning mixing elements 228.FIG. 13 is a side perspective, detail, section view of the shroudedfluid turbine 500 of FIGS. 10 and 11 cut through the inward turningmixing elements 226. The detail cross sections of FIGS. 12 and 13 depictthe ring airfoils 100 and 200 of the present disclosure incorporatedinto the mixer-ejector turbine shrouds. The ring airfoil 100 includesthe leading edge region 112, the intermediate region 115, and thetrailing edge region 116. The ring airfoil 200 includes the leading edgeregion 212, the intermediate region 215, and the trailing edge region216.

In an example, embodiment, the shrouded fluid turbine 500 may bereferred to as a mixer/ejector fluid turbine, where the airfoils 200 andairfoil 100 form an mixer/ejector pump. Referring to FIGS. 10-13, theshrouded fluid turbine 500 is supported by the support structure 302 andcomprises a turbine mixer shroud formed by an example embodiment of theairfoil 200, the energy extract assembly formed by the nacelle body 350and the rotor 340, and an ejector shroud formed by the airfoil 200. Therotor 340, airfoil 200 (i.e. turbine mixer shroud), and the airfoil 100(i.e. the ejector shroud) are coaxial with each other, i.e. they share acommon central axis 505. In an example embodiment, the airfoil 200 canbe positioned relative to the nacelle body 350 and rotor 340 usingelongate support structures 307 and the airfoil 100 can be positionedrelative to the airfoil 200 using elongate support structures 506.

In one example, embodiment the leading edge 266 of the airfoil 200 canbe positioned up stream of the rotor 340, the trailing edge 266 of theairfoil 200 can be positioned downstream of the rotor 340, the leadingedge 162 of the airfoil 100 can be disposed downstream of the rotor 340,and/or the trailing edge 166 of the air foil 166 can be positioneddownstream of the trailing edge 266. The leading edge 262 can form aninlet of the airfoil 200 in the shrouded fluid turbine 400 and thetrailing edge 266 can form the exhaust of the airfoil 200 in theshrouded fluid turbine 400.

The ejector shroud formed by the airfoil 100 includes a front end orinlet end defined by the leading edge 162, and a rear end or exhaust enddefined by the trailing edge 166.

FIG. 14 depicts the trailing edge regions 116 and 216 in more detail toillustrate example perforation 184 and 284, respectively. Theperforations 184 and 284 can be formed in the flaps 136 and 236,respectively to allow some air to flow through the flaps 136, 236 toreduce the force exerted on the flap 236 by the airflow.

FIG. 15 is a front, perspective view of another exemplary embodiment ofa shrouded fluid turbine 600 incorporating example ring airfoils 700 and800 of the present disclosure. FIG. 16 is a side, orthographic, detail,section view of the fluid turbine of FIG. 15. Referring to FIGS. 15-16,the shrouded fluid turbine 600 is supported by the support structure 302and includes the energy extracting assembly 345 having the rotor 340 andthe nacelle body 350. The ring airfoil 700 forms a turbine shroud andthe ring airfoil 800 forms an ejector shroud of the shrouded fluidturbine 600. The rotor 340, turbine shroud (i.e. the airfoil 700), andejector shroud (i.e. the airfoil 800) are coaxial with each other, i.e.they share a common central axis 605.

The airfoils 700 and 800 can be formed in a similar manner to theexample airfoils 100 and 200, as described herein. The airfoil 700 caninclude a leading edge region 712 having a leading edge 762 that forms afront end or inlet end of the airfoil 700. The leading edge region 712can have a substantially similar or identical cross-sectional structure(depicted in FIG. 16) to that of the leading edge regions 112 and 212,as described herein.

The airfoil 700 also includes a trailing edge regions 716 having atrailing edge 766 that form a rear end or outlet (exhaust) end of theairfoil 700. The trailing edge region 716 can have a substantiallysimilar or identical cross-sectional structure (depicted in FIG. 16) tothat of the trailing edge region 112, as described herein. In thepresent example, the trailing edge region 716 can have multi-sidedpolygon shape having a faceted structure. For example, the trailing edgeregions 716 can include facets 775 that are enjoined at nodes 777.

The airfoil 800 includes a leading edge region 812 having a leading edge862 that forms a front end or inlet end of the airfoil 800 and a rearend. The airfoil 800 also includes a trailing edge region 816 having atrailing edge 866 that forms an exhaust end or outlet end of the airfoil800. The airfoil 800 includes a faceted annular airfoil for which theleading edge region 812 can have a substantially similar or identicalcross section as the leading edge regions 112, 212, and 712 describedherein. In the present example, the trailing edge region 816 can havemulti-sided polygon shape having a faceted structure. For example, thetrailing edge regions 816 can include facets 875 that are enjoined atnodes 877.

The airfoils 700 and 800 can include intermediate regions 715 and 815,respectively, that extend between the leading edge regions 712 and 812,respectively, to the trailing edge regions 716 and 816, respectively.The intermediate regions 715 and 815 can be formed of intermediatesupport portions and intermediate membrane portions.

A detail cross section of the shrouded turbine of FIG. 15 is depicted inFIG. 16 and illustrates the faceted annular airfoils 700 and 800incorporated into the mixer-ejector turbine shrouds. The airfoils 700and 800 have the voluminous leading edge regions 712 and 812,respectively, that is engaged with the intermediate regions 715 and 815,respectively, which form a transitional area between the leading edgeregions 712/812 and the trailing edge regions 716/816, respectively. Arigid trailing edge region 716 is comprised of similar components asshown and described herein and provides the structure to support theintermediate membrane portions of the intermediate region 715.

In some embodiments, intermediate support portions may be incorporatedinto either or both, nodes 777 or facets 775, which are generally formedthe intimidate membrane portions. A flap 736 is engaged with thetrailing edge region 716 of the airfoil 700 to extend from the trailingedge at a fixed angle (e.g., perpendicular) with respect to the chordline of the air foil 700. Likewise, the airfoil 800 is comprised of thevoluminous leading edge region 812, the intermediate region 815, and thetrailing edge region 816. A flap 836 is engaged with the trailing edgeregion 816 of the airfoil 800 to extend from the trailing edge at afixed angle (e.g., perpendicular) with respect to the chord line of theair foil 800. The intermediate region 815 can include intermediatemembrane portions depicted as the facets 875 and nodes 877. Intermediatesupport portions 839 of the intermediate region 815 can be dispersedradially about the central axis 705 and also engage with the airfoil 700to connect the airfoil 700 to the airfoil 800.

FIG. 17 depicts a front perspective view of an example shrouded fluidturbine 900 in the form of a wind turbine having the support structure302, the energy extracting assembly 345 and a turbine shroud formed bythe example airfoil 700 having the leading edge region 712, theintermediate region 715, and the trailing edge region 716. The energyextracting assembly 345 can include a nacelle body 350 and a rotor 340.The rotor 340 is engaged with the nacelle body 350 at the proximal endof the rotor blades. The airfoil 700 can encircle the rotor 340. In oneexample, embodiment the leading edge 766 of the airfoil 700 can bepositioned up stream of the rotor 340 and/or the trailing edge 766 ofthe airfoil 700 can be positioned downstream of the rotor 340. Theleading edge 762 can form an inlet of the shrouded fluid turbine 900 andthe trailing edge 766 can form the exhaust of the shrouded fluid turbine900. The flap 736 can allow a fluid flow (e.g., airflow) flowing alongthe inner surface of the air foil to remain attached to the innersurface. In an example embodiment, the airfoil 700 can be positionedrelative to the nacelle body 350 and rotor 340 using elongate supportstructures 307 such that the nacelle body 350, the rotor 340, and theairfoil 100 are position coaxially with respect to each other about thecenter axis 605.

Example embodiments of the present disclosure advantageously provide aringed airfoil having a generally lightweight structure relative toconventional ringed airfoils. Example embodiments of the airfoilincluding the flap can result in a ringed airfoil that exhibits similarperformance characteristics as a conventional airfoil with a greaterchord length and no flap. Furthermore, example embodiments of thepresent disclosure provide for generally easier and less time consumingmaintenance and repair of the airfoils as compared to conventionalairfoils, particularly with respect to the maintenance and repair of theintermediate membrane portions and the flap.

As set forth previously, the present embodiment is not specific to anejector of a MET and may be applied to those ducted or shrouded fluidturbines as understood in the art. The present disclosure has beendescribed with reference to example embodiments. Obviously,modifications and alterations will occur to others upon reading andunderstanding the preceding detailed description. It is intended thatthe present disclosure be construed as including all such modificationsand alterations insofar as they come within the scope of the appendedclaims or the equivalents thereof.

We claim:
 1. An aerodynamically contoured ring airfoil comprising; abody extending circumferentially about a center axis having anaerodynamic structure formed by an outer surface and an inner surface,the outer and inner surfaces extend axially with respect to the centeraxis along a camber line, the body including a leading edge region, atrailing edge region, and an intermediate region extends between theleading edge region and the trailing edge region; the leading edgeregion having a non-uniform cross-sectional thickness extending alongthe camber line defined by the outer surface and the inner surface ofthe body; and the trailing edge region including a flap extendingtherefrom and orientated at an angle with respect to a chord line of thebody to allow a fluid flow flowing along the inner surface to remainattached to the inner surface.
 2. The airfoil of claim 1, wherein theflap extends from the trailing edge region perpendicularly to the chordline.
 3. The airfoil of claim 1, wherein the length of the flap is aboutone-tenth to about one-third a length of the chord line.
 4. The airfoilof claim 1, wherein the flap includes at least one perforation to permitfluid flow through the flap.
 5. The airfoil of claim 1, wherein the flapextends from a trailing edge of the airfoil.
 6. The airfoil of claim 1,wherein the flap extends between a first ring structure and a secondring structure, the first and second ring structures providing a hoopstrength to the flap.
 7. The airfoil of claim 6, wherein the first ringstructure provides a hoop strength to the trailing edge region of thebody.
 8. The airfoil of claim 1, wherein the intermediate regioncomprises at least one intermediate support portion extending betweenthe leading edge region and the trailing edge region.
 9. The airfoil ofclaim 8, wherein the intermediate support portion is composed of a rigidmaterial.
 10. The airfoil of claim 8, wherein the intermediate supportportion has a uniform cross-sectional thickness extending along the meancamber line defined by the outer surface and the inner surface of thebody.
 11. The airfoil of claim 8, wherein the intermediate regioncomprises at least one intermediate membrane portion extending betweenthe leading edge region and the trailing edge region.
 12. The airfoil ofclaim 11, wherein the intermediate membrane portion has a uniformcross-sectional thickness extending along the mean camber line definedby the outer surface and the inner surface of the body.
 13. The airfoilof claim 11, wherein the intermediate region is composed of a non-rigidmaterial.
 14. The airfoil of claim 11, wherein the intermediate supportportions provides structural support to the intermediate membraneportion.
 15. An energy extracting shrouded fluid turbine comprising: anenergy extracting assembly including a rotor disposed radially about acenter axis; and an airfoil having a body extending circumferentiallyabout the center axis, the body having an aerodynamic structure formedby an outer surface and an inner surface, the outer and inner surfacesextend axially with respect to the center axis along a camber line, thebody including a leading edge region, a trailing edge region, and anintermediate region extends between the leading edge region and thetrailing edge region; the leading edge region having a non-uniformcross-sectional thickness extending along the camber line defined by theouter surface and the inner surface of the body; and the trailing edgeregion including a flap extending therefrom and orientated at an anglewith respect to a chord line of the body to allow a fluid flow flowingalong the inner surface to remain attached to the inner surface.
 16. Thefluid turbine of claim 15, wherein the flap extends from the trailingedge region perpendicularly to the chord line.
 17. The fluid turbine ofclaim 15, wherein the length of the flap is about one-tenth to aboutone-third a length of the chord line.
 18. The fluid turbine of claim 16,wherein the flap includes at least one perforation to permit fluid flowthrough the flap.
 19. The fluid turbine of claim 15, wherein the flapextends from the trailing edge region of the airfoil, the flap extendingbetween a first ring structure and a second ring structure, the firstand second ring structures providing a hoop strength to the flap and thefirst ring structure providing a hoop strength to the trailing edgeregion of the body.
 20. The fluid turbine of claim 15, wherein theintermediate region including at least one intermediate support portioncomposed of a rigid material and at least one intermediate membraneportion composed of a non-rigid material, the intermediate supportportion and the intermediate membrane portion extending between theleading edge region and the trailing edge region.
 21. The fluid turbineof claim 20, wherein at least one of the intermediate support portion orthe intermediate membrane portion has a uniform cross-sectionalthickness extending along the mean camber line defined by the outersurface and the inner surface of the body.